UV radiation has recently been classified as a known human carcinogen by the US Department of Health and Human Services. Nevertheless, the voluntary exposure to sunlight continues unabated despite progressively increasing rates of ultraviolet radiation (UVR)-induced illness and death, particularly skin cancer. An increasingly common form of UVR administration is through the use of indoor tanning salons. Almost 30 million Americans, including 20% of 18-39 year olds, visit indoor tanning salons each year. Frequent and excessive tanning, despite a growing understanding by those who tan of the morbidity and mortality associated with tanning, suggests that UVR may impart rewarding effects beyond the assumed cosmetic benefits. Recent studies, in fact, have shown that up to 40% of both frequent beach and salon tanners exhibit signs and symptoms consistent with an addictive disorder, including an inability to decrease their tanning frequencies, compulsive tanning, and/or continued tanning despite adverse consequences. To empirically measure putative centrally rewarding properties of UVR, we assessed the effects of a commercially available tanning bed upon regional cerebral blood flow (rCBF), a measure of brain activity, using single-photon emission computed tomography (SPECT). Compulsive salon bed tanners were placed under a UVA/UVB tanning light during two sessions; one session with active UVR and the other with filtered UVR (sham UVR). During the active UVR session, relative to sham UVR session, subjects demonstrated both a significant decrease in Desire to Tan and a relative increase in rCBF of the dorsal striatum (including caudate and putamen), anterior insula, and medial orbitofrontal cortex. These preliminary findings suggest that UVR may have centrally rewarding properties that encourage excessive tanning. As the mesostriatal dopaminergic pathway plays a key role in reward and addiction, we propose to extend these novel findings by using 123I-IBZM to determine if 1) dopamine is released during UVR (as is observed in response to other rewards), 2) basal D2/D3 receptors are lower in compulsive tanners relative to infrequent tanners (a finding commonly observed in other addictive disorders), and 3) whether dopamine efflux in response to UVR, relative to sham UVR, differs between compulsive and infrequent tanners. If our hypotheses are proven correct, these findings will support a dermatologic-mesostriatal reward pathway, confirm a neurobiological, reward-based mechanism for compulsive tanning behaviors, demonstrate underlying biological characteristics similar to other addictive disorders (supporting an addiction diagnosis for compulsive tanners), offer a framework for future studies to examine dermatologic-mesostriatal pathways, and provide a rationale for the development of pharmacological treatments for compulsive tanning. Data obtained by the R21 mechanism will also inform prospective studies regarding the power necessary to demonstrate statistical significance between hypothesized comparisons not reaching significance in this preliminary study. PUBLIC HEALTH RELEVANCE: Exposure to tanning beds continues unabated despite progressively increasing rates of ultraviolet radiation- induced illness and death, particularly skn cancer. Frequent and excessive tanning, in spite of a growing understanding by the general population (as well as by those who tan) of its associated morbidity and mortality, suggests that the ultraviolet radiation from sunlight and tanning beds may impart rewarding effects beyond the assumed cosmetic benefits. An understanding of the central nervous system reward mechanisms involved in excessive tanning will provide targets for treatment interventions to decrease excessive tanning.